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<h3 class="docSection1Title">Chapter 17</h3>
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<P><table border="0" cellspacing="16" cellpadding="0"><tr valign="top"><TD align="right" class="docText" width="50"><a name="ch17qa1q3a1"></a><B><a class="docLink" href="ch17lev1sec8.html#ch17qa1q3">17.3</a></b></TD><td><p class="docText">A <span class="docEmphasis">declaration</span> specifies the attributes (such as the data type) of a set of identifiers. If the declaration also causes storage to be allocated, it is called a <span class="docEmphasis">definition</span>.</P>
<p class="docText">In the <tt>opend.h</tt> header, we declare the three global variables with the <tt>extern</tt> storage class. These declarations do not cause storage to be allocated for the variables. In the <tt>main.c</tt> file, we define the three global variables. Sometimes, we'll also initialize a global variable when we define it, but we typically let the C default apply.</P></TD></tr><TR valign="top"><td align="right" class="docText" width="50"><a name="ch17qa1q5a1"></a><B><a class="docLink" href="ch17lev1sec8.html#ch17qa1q5">17.5</a></b></TD><TD><p class="docText">Both <tt>select</tt> and <tt>poll</tt> return the number of ready descriptors as the value of the function. The loop that goes through the <tt>client</tt> array can terminate when the number of ready descriptors have been processed.</p></TD></TR></table></p>

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